Abstract: Aims The root economic spectrum helps explore the trade-offs between resource acquisition strategies and lifespan of fine-roots of different orders, providing essential insights into the relationships among root traits and the mechanisms of species' adaptation under local environments. Methods This study investigates 30 shrub species with different life forms (evergreen and deciduous) suitable for the severely degraded karst region. Using the root order grading method, we analyzed the morphology, nutrients and stoichiometric ratios of 1-3 order fine-roots among different life forms. We aimed to understand the variations in morphology and nutrients across different root orders and explore the survival strategies and variation dimensions of fine-roots in different life forms, searching for the presence of a root economic spectrum. Important findings The results showed that (1) the average contents of carbon, nitrogen, and phosphorus in fine-roots of 30 karst shrubs (438.67 mg/g, 5.16 mg/g, and 0.31 mg/g, respectively) were lower than the average contents in fine-roots of Chinese plants (473.9 mg/g, 9.16 mg/g, 1.03 mg/g). Among 1-3 order fine-roots, the coefficient of variation for carbon content was minimal (1%), while phosphorus content showed the largest variation.(2) The phosphorus content in fine-roots of 30 evergreen shrubs was significantly lower than that of deciduous shrubs, indicating that evergreen shrubs in karst areas are more prone to phosphorus limitations compared to deciduous shrubs. (3) Root diameter and specific surface area showed a highly significant negative correlation only in the third-order fine-roots of deciduous shrubs, while evergreen shrubs exhibited significant negative correlations across 1-3 order fine roots. (4) PCA results indicate that variations in fine-root traits of 30 karst shrubs can be decomposed into multiple principal components. The first principal component mainly includes morphological traits such as specific root surface area, average diameter, specific root length, fine -root biomass, and root tissue density. The second principal component mainly reflects nutrient factors, corresponding to fast and slow resource acquisition strategies. This demonstrates the existence of a root economic spectrum among the 30 karst shrubs.The conclusions facilitate a deeper understanding of the ecological strategies of shrub adaptation to rocky desertification habitats in karst regions and further recognize the nutrient utilization strategies of suitable shrubs in these areas.

Key words: root order, fine-roots of shrubs, karst, PCA analysis, root economic spectrum